It is well known that the probability of surviving a heart attack often depends critically on the speed with which appropriate medical care is provided. One of the most common and life threatening consequences of a heart attack is the development of a cardiac arrhythmia such as ventricular fibrillation in which the heart is unable to pump a significant volume of blood. When such an arrhythmia occurs, serious brain damage and death will invariably result unless a normal heart rhythm can be restored within a few minutes.
The most effective treatment for ventricular fibrillation is the application of a strong electric shock to the victim. By a mechanism not fully understood, such an electric shock frequently terminates the chaotic activity characteristic of arrhythmias, and restores the normal pumping action of the heart. Defibrillators for producing and delivering such shocks have been known and successfully used for many years. However, the size and cost of prior defibrillators, coupled with the risk they pose if used improperly, have restricted the use of defibrillators to hospitals and to emergency medical facilities. Many lives would be saved each year if defibrillators could be made more immediately available to heart attack victims.
A large number of heart attacks occur to people who have a history of cardiac problems, and who are therefore known to be at risk. In recent years, many family members of high risk patients have received training in cardiopulmonary resuscitation, a technique designed to maintain some blood flow even if the heart is in fibrillation or has stopped beating altogether. Such training is helpful because a large percentage of repeat heart attacks occur in the presence of a family member. Unfortunately, it has to date not been possible to provide the family members of high risk patients with access to the generally more effective technique of defibrillation, because of the difficulty of designing a defibrillator that is portable and that can be safely and effectively used by nonmedical personnel.